Efficacy and predictors of response of nivolumab in treatment-refractory MSI solid tumors: Results of a tumor-agnostic DRUP cohort.
Authors: Birgit Geurts, Laurien Joanna Zeverijn, Thomas W. Battaglia, Joris van de Haar, Jade M. van Berge Henegouwen, Louisa Rose Hoes, Hanneke van der Wijngaart, Paul Roepman, Wendy W.J. de Leng, Anne M.L. Jansen, Vincent van der Noort, Myriam Chalabi, Lot A. Devriese, Carla M.L.- Van Herpen, Hans Gelderblom, Henk M.W. Verheul, Emile E. Voest
Journal: Journal of Clinical Oncology (2023)

2590 Background: Microsatellite unstable (MSI) tumors represent 4% of all cancer diagnoses and are known to be sensitive to immune checkpoint inhibitors (ICI). Despite the progress made, a significant proportion of patients with MSI tumors does not respond, highlighting the urgent need to identify additional predictive biomarkers. In this study, we evaluated the efficacy of the PD-1 inhibitor nivolumab across pre-treated solid MSI tumors and performed extensive biomarker analysis to better characterize ICI-effectiveness in this setting. Methods: Adult patients with MSI tumors who exhausted all standard of care treatment options were eligible for inclusion and were enrolled in the Drug Rediscovery Protocol (DRUP), a clinical trial that treats cancer patients with approved targeted- and immunotherapies outside their registered indication, based on their tumor molecular profile (NCT0295234). Patients were treated with nivolumab (four cycles of 240 mg every 2 weeks, followed by 480 mg every 4 weeks) until disease progression or unmanageable toxicity. Primary endpoint was clinical benefit (CB, objective response (OR) or stable disease ≥ 16 weeks). Whole genome sequencing and RNA sequencing were performed on pre-treatment biopsies to reveal potential predictors of response or resistance to anti-PD1. Results: 130 evaluable patients were enrolled with in total 16 different tumor types. CB was observed in 62% (95% CI 46 – 54) ( N = 80) with an OR in 45% (95% CI 53 – 70) ( N = 58). After a median follow-up of 14.5 months (95% CI 13 – 19), median progression free survival was 18 months (95% CI 9 – not reached) and median overall survival was not reached. HLA class I status and mutational burden were not significantly associated with CB. However, in depth biomarker analyses identified that mutational burden was predictive of CB in HLA-wildtype patients (52%) but not in HLA class I mutants (48%). Strikingly, in contrast to the paradigm that neoantigen-specific adaptive immunity is primarily involved in clearing MSI tumors, transcriptomics indicated that, compared to non-CB, CB was characterized by significantly higher expression of key modulators in innate immunity, including non-classical HLA transcripts (P = 4.2x10 -3 ), NKGD2 ligands MICA/MICB (P = 6.4x10 -3 ), killer immunoglobulin-like receptors ( P = 0.047) and butyrophilins ( P = 0.024). Conclusions: Nivolumab proved highly effective in pre-treated, advanced solid MSI tumors. Genomic analysis revealed that neoantigen burden only determined ICI-effectiveness in patients with wildtype HLA class I. Furthermore, transcriptomics revealed a central role of innate immunity in ICI-effectiveness in MSI tumors, which aligns with the fact that these tumors frequently lose HLA class I antigen presentation. Together, these results inform novel biomarker strategies to further refine precision medicine in this patient population. Clinical trial information: NCT0295234 .